Percolation Test

Percolation test – surface water drainage

You need to do a percolation test if your thinking of having a soakaway drainage system in your garden or replacing a soakaway system. A percolation test must also be done for septic tanks/ sewage treatment.

Make sure you do this test in normal conditions and not in summer. AS the water table will be higher in winter.

Dig a hole to find the water table level in your property.

Find 2 test locations, at the point you want to install/refurb your soakaway system and at the depth you want for the system too.  Dig the holes 300mm at least below any infill pipe will be.

Fill the test holes with water, check at 6 and 12 hours. If the water has not drained this is a failed test.

You can go further by filling your test holes with water again and working out how long it does take for water to drain from a 225mm to 150mm. This should be repeated for create an average timing. This will give you a measure of how long your water takes to drain by 1mm per second. So divide the time it takes for the water to filter away in seconds from 225mm to 1500mm and divide by 150. Any result between 15-100 seconds means a suitable soil for a soakaway/ drainage system.

Please remember soakaway systems are not for foul water. There are also other things to consider after doing your percolation test regarding siting your soakaway crates at least 2.5m away from a boundary and at least 5m form a wall of a building, or for use under areas of vehicular traffic. Some councils in England also have specific rules for their area, such as needing a percolation test done by a company before works cn begin.

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